1. Field of the Invention
This invention relates to a motor assembly, more particularly to a motor assembly which includes a dc motor and a driving unit for driving the dc motor at different speeds.
2. Description of the Related Art
A conventional motor assembly usually includes an induction motor and a variable frequency device. The aforementioned conventional motor assembly has the following disadvantages:
1. The induction motor assembly is relatively large, and the noise that is generated during operation is relatively loud. Furthermore, the cost of the induction motor assembly is relatively high. PA1 2. The variable frequency device varies the current for the induction motor so as to enable the induction motor to rotate at different speeds. However, the torque ratio thus obtained is relatively low. Therefore, the problem of an insufficient torsional force is present when the motor speed is relatively low. PA1 3. The induction motor usually comprises a rotor which includes a rotatable shaft and a plurality of fan-shaped permanent magnets attached to the rotatable shaft by means of adhesives. Therefore, undesired disengagement of the permanent magnets from the rotatable shaft may occur during the rotation of the rotatable shaft. Furthermore, the unique shape of the permanent magnets results in a higher processing cost and complicates the assembling process.